1. Field of the Invention
The present invention relates generally to the field of cutting tools, and in particular to a cutting tool for cutting composite material, such as composite honeycomb core material. The honeycomb core material can be of the type comprising aramid fiber with a phenolic resin or fiberglass fibers with phenolic resin.
Honeycomb core is generally made from a series of hexagonal cells, nested together to form panels similar in appearance to a cross-sectional slice of a beehive. A basic characteristic of honeycomb core is that it posseses a high strength-to-weight ratio in the axial direction of the cell structure and a low strength in the transverse direction of the cell structure.
2. Prior Art
In the past it has been difficult to quickly and accurately machine irregular shapes, such as for example interior cut-outs, pockets, holes or bevels, in, for example, composite honeycomb core material. The noted irregular shapes requires any one or more of the following types of cutting: pocket milling, plunge cutting, and bevel cutting. Pocket milling refers to the removal of material in a plane such that a cavity, hollowed out space, or cornered step is created. Plunge cutting refers to creating a hole in the material by driving the cutter tool in a downward motion into, but not necessarily through the material. Finally, bevel cutting refers to a type of cutting whereby two relatively parallel surfaces are connected by an inclined or angular surface.
At the present time, the production of some irregular shapes is done by tedious hand sanding techniques. While the results can be quite satisfactory, the time and costs involved are simply prohibitive.
Experience has shown that the material comprising composite honeycomb core; such as for example aramid fiber or fiberglass mixed with a phenolic resin, tends to deflect, bend or tear before being cut by the shearing action of the cutting edge of a conventional milling cutter. The deflecting, bending or tearing is a result of the low strength of the honeycomb core in the transverse direction of the cell structure and the high elasticity and shear resistance of the materials in composite honeycomb core.
Attempts to produce the noted irregular shapes by using a milling machine equipped with a valve stem cutter were unsuccessful. Valve stem cutters, which are used for cutting thin, small slices of material from the top surface of honeycomb core, do not possess the design characteristics required for pocket milling, plunge cutting or bevel cutting and are therefore limited in the types of irregular shapes that can be produced.
A search of the market for a commercially available cutting tool for machining irregular shapes and capable of producing relatively burr-free surfaces, i.e., a surface where the burr height is less than 0.020 inches determined that none were available.
Since a tool was not available on the market which would achieve the surface finish having the standard burr height noted above, it was decided to design a tool specifically for the purpose.